A combination cigarette filter manufacturing machine comprises a combining unit for forming groups of filter portions, each comprising at least two different filter portions aligned axially and contacting end to end; a wrapping unit, which receives a succession of groups of filter portions from the combining unit, wraps a strip of wrapping material about the succession of groups of filter portions to form a continuous filter rod, and cuts the combination filters from the continuous filter rod by cyclically cutting the continuous filter rod crosswise; and a transfer unit, which transfers the groups of filter portions from the combining unit, in which the groups of filter portions travel crosswise (i.e. perpendicularly to their axes), to the wrapping unit, in which the groups of filter portions travel axially (i.e. parallel to their axes). In other words, the transfer unit alters the way in which the groups of filter portions travel, by receiving them travelling crosswise, and releasing them travelling axially.
Known transfer units comprise at least one release drum, which receives the groups of filter portions from the combining unit; and a transfer drum, which removes the groups of filter portions from the release drum, and feeds them successively onto a forming beam of the wrapping unit. On known transfer units, the transfer drum is a “spider” type, i.e. has a number of suction pickup heads, which are rotated about a central axis of rotation, remaining parallel to themselves at all times, and are fitted to supporting arms projecting axially, i.e. from the end wall, of the transfer drum.
To increase output (i.e. the number of items produced per unit of time) while at the same time improving quality, “twin-line” wrapping units have been proposed, i.e. having a horizontal forming beam with two parallel grooves, in each of which a respective strip of wrapping material is wrapped about a continuous succession of groups of filter portions. In this case, the transfer unit comprises two release drums, which divide the groups of filter portions from the combining unit into two streams; and the transfer drum has “twin” suction seats, each of which removes two groups of filter portions simultaneously from the two release drums, and feeds them simultaneously onto the forming beam of the wrapping unit. Examples of transfer units of this sort are described in Patent Applications EP1787534A1 and EP2145552A2.
On transfer units with two release drums, however, installing a “spider” type transfer drum poses serious problems, on account of the inevitable size of the release drums. That is, the transfer drum must be located a fairly long distance from the release drums, which means the supporting arms projecting axially from the transfer drum to support the suction pickup heads are substantially Z-shaped and, more importantly, extremely long, thus making it difficult to position the suction pickup heads accurately when the transfer drum is rotating. Moreover, as the transfer drum rotates, the suction pickup heads tend to vibrate slightly and spin out of position; and, because of the length and shape of the supporting arms, suction to the pickup heads is not as effective as it should be, on account of the long, “winding” route, and therefore serious load losses and pneumatic inertia, of the pneumatic circuit of each pickup head (i.e. a considerable time lapse exists between suction being activated/deactivated at the start of the pneumatic circuit, and being activated/deactivated at the corresponding pickup head.